Variable-pitch airscrew



Oct. 26, 1943. L., G. FAlRHuRsT ET AL 2,332,786

VARIABLE-FITCH AIRSCREW Filed Feb. 17, 1942 mz, fana/7d ab' M' 22 @Qfziarxfrzf ma@ ra' Patented Oct. 26, 1943 VARIABLE-FITCH AIBSCREW Leonard Gaskell -Fairhurst and Herbert Newport, Gloucester, England, assignors to Roto! Air-screws Limited, Gloucester, England, a company of Great Britain application February 1v, 1942, serial No. 431,308 In Great Britain September 20, 1940 1 Claim. (CL 17o-163) This invention is concerned with variable-V pitch airscrews of the type in which an hydraulic ram is used to adjust the pitch of the blades under the control of a governor unit controlling the supply of the pressure-fluid to the ram.

Unless an adjustable blade in an airscrew is controlled, it tends to set itself into a fine-pitch position under the centrifugal and aerodynamic forces acting on it; this is undesirable as if the control is lost it leads to excessive engine-speed and to the necessity of reducing the enginepower; the control maybe lost temporarily by the engine cutting-out in some abnormal condition of flight, as when flying inverted or on going into a very steep dive, and also a permanent loss of control may arise from accident or damage from enemy action, and in this case it is still more important that the blades should be prevented from automatically assuming a finepitch position.

l'n an hydraulically controlled airscrew of the type above-described, the ram-cylinder is normally filled with a working uid on both sides of the ram and when pressure-fluid is admitted to one side to effect an adjustment of pitch, fluid is forced out from the other side by the movement of the ram in its cylinder and it will, therefore, be `appreciated that in the circumstances mentioned above, when the pilots control of the airscrew is lost, the automatic or self-adjustment of a blade to its fine-pitch position, causes the working fluid to be discharged from one side of being lost, there is provided, according to another feature of this invention, an additional port giving communication to and from the chamthe ram-chamber, the pressure available to eiect this being derived from the forces acting upon the blade.

According to this invention, there is provided in a variable-pitch airscrew of the type described, the combination with the chamber from which liquid is delivered by the self-adjusting movement aforesaid of the blade, of means for admitting fluid under pressure to said chamber, and an outlet valve from said chamber, which outlet valve is loaded to a pressure greater than can be exerted on the fluid by the self-adjusting movements of the blade, but less than the working pressure used for effecting adjustment of the blade in normal working.

The supply of working fluid to this chamber is preferably effected by means of another port controlled by a simple non-return valve which permits entry of the fluid but completely prevents delivery from the chamber.

In order: to permit rapid adjustment of the blade, and to provide for setting the blade at a suitable pitch in the event of the pitch-control ber, and a valve controlling said port and means whereby the valve which is normally open is moved to its closed position when the blade reaches a predetermined position in lts movement towards a fine-pitch setting.

In the accompanying drawing which illustrates the application of this invention to a Rotol (registered trade-mark) hydraulic constant-speed variable-pitch airscrew,

Figure 1 is a central longitudinal section of the hydraulic ram and cylinder, and

Figure 2 is a detail, being a section on the line II-II of Figure 1.

The hydraulic apparatus comprises a ram I0 carried on a stationary hollow shaftv Il coaxial with the airscrew-blade, and a cylinder I2 which is mounted to move relatively to the ram I0 is coupled by rods I3 to the blades of the airscrew to adjust their pitch. Movement of the cylinder towards the left in Figure 1 adjusts the blades towards a coarser-pitch position, and movement towards the right adjusts them towards a finerpitch position.

The ram I0 divides the cylinder into two chambers I4, I5 respectively and the working liquid is supplied to and from the chamber I4 through a central bore I6 in the shaft Il; the chamber I5 has the liquid supplied to and from it through the annular space Il between a hollow shaft I8 and the shaft Il aforesaid, this annular space II opening into the chamber I5 by means of ports I9. When liquid is supplied under pressure to either of the chambers Il, I5 to move the cylinder. a corresponding quantity of liquid is forced out form the other chamber through the appropriate conduit.

This invention is concerned with the construction and arrangement of valves controlling communication between the conduit I6 aforesaid and the chamber I4, since this is the chamber from which liquid is forced out by the self-adjusting movement of the blades when the pitchcontrol is lost, and it is desirable to prevent or limit such self-adjusting movement.

A valve housing indicated generally by the reference 20 is secured on the end of the shaft II and serves to retain the ram I0 thereon. The hollow interior of this casing which is in free communication with the passage I6 is provided with ports 2| (Figure 2) controlled by non-return valves 22, which are lightly spring-loaded on to their seats the arrangement being such that liquid supplied through the conduits I8 under pressure opens the valves 22 and delivers the liquid into the chamber I4.

There is also provided a restricted port 23 (Figure 2i which opens from the chamber Il to the interior oi! the casing 20 under the control of a valve 2l which is loaded by a spring 3D to a high pressure, greater than can be exerted on the liquid in the chamber I4 by the self-adjusting movement oi' the blades towards their nue-pitch setting. This loading however is less than the working pressure of the fluid for normal operation. By way ot example, the normal working pressure of th'e liquid may be 350 lbs. per square inch, the loading oi' the valve 24 may be 150-175 lbs. per square inch and the loading of the valves 22 may be about 10 lbs. per square inch.

When liquid under pressure'is supplied to the to be moved inward. After a predetermined amount-oi such' movement the outer plate I4 strikes 25 and closes this valve, thus preventing the blades from reaching an undesired low Y pitch. However, if a still lower pitch is desired the pressure in I5 is increased until the pressure in I l becomes sumcient to open valve 24.

Whilst a particular construction and arrangement of valves has been described in connection g with the above it will be undesrstood that varichamber I5 to move the cylinder I2 to the right, 20

the liquid in the chamber It has to be discharged therefrom, and as so far described the only path of discharge is by way of th'e loaded valve 24, but this single outlet slows ,the efi'ective operating pressure in4 I5 and in order to 25 increase the rate' of evacuation in Il for all normal operations, there is provided an additional valve controlling a port 26 which provides communication from the chamber I4 through a tube 21 to th'e conduit I6. This valve is held 30 in its open position by a light spring 2E and is so positioned that when the cylinder I2 moves towards the right, it engages the valve 25 and moves it to close the port 26 and thereby shut off this communication. 'I'he parts are so pro- 35 portioned that this closing ofthe valve takes place when the blades are in a medium pitch setting suitable for use when the pitch-control is lost as mentioned above, being for example 15 away from the iinest pitch' setting. In order to permit the possibility of adjustment to the finest pitch position, the tube 21 with the valve 25 is movable towards the right against the action of the spring 29. It will be appreciated that during this part of themovement the liquid is delivered from the chamber Il by way of the port 23. When the blades are turned toous other types and arrangements can be used to operate in the same manner. It will be seen that with the arrangement above described there are two inlet valves 2i, and two outlet valves 24, 2e respectively so that there is little likelihood of the whole device being rendered inoperative by the sticking of a valve.

We claim:

In a hydraulically-operated variable-pitch airscrew, the combination of blades rotatable each about its longitudinal axis to vary its pitch, a double-acting hydraulic ram coupled to said blades, means for admitting pressure-huid through a non-return valve to one chamber of the ram to move the blades in a direction opposite to that inwhich they move under centrifugal and aerodynamic forces if unconstrained, an outlet valve from said chamber, a spring-loading-for said outlet valve which is greater than the pressure that can be exerted on the uid by the self-adjusting movements of the blades but less than the working pressure used for effecting adjustment of the blades in the opposite direction, means for admitting fluid to and discharging it from the other chamber of said ram at will, an additional port communicating with said first chamber, a valve controlling said port, and means adapted to be engaged by a movable part oi said ram to close said valve when th'e blades reach a predetermined position in their movement towards a line-pitch setting.

LEONARD` GASKELL FAIRHURST.

ERT ORT. 

